1. Field of the Invention
This invention relates generally to the field of semiconductor device manufacturing and, more particularly, to a method and apparatus for classifying faults based on wafer state data and sensor tool trace data.
2. Description of the Related Art
To fabricate a semiconductor device, a wafer is typically processed in numerous processing tools in a predetermined sequence. The processing tools may include photolithography steppers, etch tools, deposition tools, polishing tools, rapid thermal processing tools, implantation tools, and the like. Each processing tool modifies the wafer according to a particular operating recipe. For example, a photolithography stepper may be used to form a patterned layer of photoresist above the wafer. Features in the patterned layer of photoresist correspond to a plurality of features, e.g. gate electrode structures, which will ultimately be formed above the surface of the wafer. The tool sequence, as well as the recipes used by the tools, must be carefully controlled so that the features formed on the wafer meet appropriate design and performance criteria. Thus, advanced process control (APC) systems are often used to coordinate operation of the processing tools.
A conventional APC system includes one or more machine interfaces that are communicatively coupled to equipment interfaces associated with each of the processing tools. The machine and equipment interfaces are typically computers or workstations that are coupled to a network. For example, a plurality of processing tools may be coupled to an Intranet via an associated plurality of equipment interfaces. A machine interface that implements the conventional APC system may also be coupled to the Intranet. In operation, the conventional APC system initiates a control script based upon a manufacturing model, which can be a software program that automatically retrieves the data needed to execute a manufacturing process, and transmits one or more control messages, such as the operating recipe, to the processing tools.
The processing tools typically include one or more sensors to collect data associated with operation of the processing tool. For example, an etching tool may include a sensor to monitor the radio frequency power delivered by the etching tool. For another example, a rapid thermal anneal tool may include a thermocouple to monitor a temperature within the tool. The data acquired by the various sensors may be referred to as tool trace data. The collected tool trace data may then be provided to the APC system, which may use the collected tool trace data for various purposes such as fault detection and/or classification. For example, the tool trace data collected by the thermocouple in the rapid thermal anneal tool may indicate that the temperature within the tool has dropped below a desired threshold, indicating a possible fault.
Wafer state data indicative of the physical state of one or more wafers may also be collected by various devices within the APC system. For example, one or more metrology tools may be used to perform ex situ measurements on selected wafers after they have been processed by one or more processing tools. The ex situ measurements may include measurements of a thickness of a layer of material formed on the wafer, a critical dimension (CD) of one or more features formed on the wafer, and the like. One or more in situ measurements may also be performed by devices incorporated within a processing tool. The in situ measurements may include measurements of a temperature of the wafer, a thickness of a layer formed on the wafer, a critical dimension of one or more features formed on the wafer, or other characteristic parameters that may be measured while the wafer is within the processing tool. The collected wafer state data may then be provided to the APC system, which may use the collected wafer state data to detect faults associated with the processing. For example, the wafer state data collected by an ex situ metrology tool may indicate that a mean critical dimension of one or more features exceeds a desired threshold value for the mean critical dimension, indicating a possible fault.
However, conventional APC systems treat the sensor tool trace data and the wafer state data as independent data sets. This approach may limit the ability of conventional APC systems to diagnose and/or classify faults that may occur in one or more processing tools. For example, a fault such as an unexpected change in a gas flow rate or a temperature in an etching tool may increase the mean critical dimension of the one or more features formed on the wafers in a wafer lot processed in the etching tool. Thus, information indicative of the fault may be present in both the sensor tool trace data set and the wafer state data set. However, the ability of the conventional APC system to detect and/or classify this fault may be limited by the system's inability to associate the relevant portions of the sensor tool trace data set and the wafer state data set.
The present invention is directed to addressing the effects of one or more of the problems set forth above.